The present invention relates generally to gas turbine engines, and, more specifically, to exhaust nozzles therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Energy is extracted from the gases in a high pressure turbine (HPT) for powering the compressor, and further energy is extracted in a low pressure turbine (LPT) which powers a fan in a turbofan aircraft engine configuration.
In a turbofan engine, a substantial portion of the air pressurized by the fan is used for providing propulsion thrust for powering an aircraft in flight. A portion of the fan air is further pressurized in the compressor for generating the combustion gases which are also discharged from the engine to provide additional thrust.
The engine may include two separate exhaust nozzles, one for the fan air and one for core exhaust, which both discharge their exhaust flows together into the ambient external airstream for propelling the aircraft during flight.
The high velocity engine exhaust flow mixes with the ambient airflow and generates considerable noise during aircraft takeoff and climb from an airport. Government regulations limit noise levels, and are a significant design objective especially for more powerful aircraft engines.
Various noise attenuation features have been developed over the history of modern aircraft engines but typically add weight and cost to the engine, and can adversely affect overall engine performance and efficiency of operation.
A modern noise attenuation exhaust nozzle is disclosed is U.S. Pat. No. 6,360,528 assigned to the present assignee. The chevron nozzle in this patent has a serpentine triangular trailing edge and separates internal and external flowstreams. The chevron nozzle is a relatively thin, single-ply sheet metal shell which permits the relatively slow velocity external flow to mix with the higher velocity internal core flow for substantially reducing the velocity thereof, and correspondingly reducing noise.
The chevron nozzle is being developed specifically for reducing noise in subsonic commercial aircraft engines which require maximum efficiency of operation, yet such noise reduction does not significantly compromise engine efficiency due to the simple and lightweight chevron nozzle.
However, supersonic business jet (SSBJ) engines are presently being developed for achieving supersonic cruise operation of commercial aircraft. Supersonic operation of the aircraft requires considerably more powerful aircraft engines, and increases the difficulty of noise attenuation.
Since the SSBJ engine must operate both subsonically and supersonically, the engine must be operated with a variable cycle for maximizing efficiency across the large speed range. A convergent-divergent (CD) exhaust nozzle, which is typically variable, is typically used for supersonic engines with and without afterburners or combustion augmenters.
Subsonic commercial aircraft typically have turbofan engines with converging exhaust nozzles operating up to about a nozzle pressure ratio of 4. Supersonic turbofan engines are typically designed with higher nozzle pressure ratios exceeding 4, and utilize the CD nozzle for optimizing performance.
The CD nozzle is inherently more complex than the simpler converging subsonic nozzle, and has a greater need for noise attenuation due to the increased velocity of the exhaust flow.
Accordingly, it is desired to provide an improved exhaust nozzle for attenuating noise in the differently configured exhaust nozzle of a supersonic aircraft engine.